Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. The minimum temperature to which water can be cooled in a cooling tower is

Dew point temperature of air

Ambient air temperature

Wet bulb temperature of air

Dry bulb temperature of air

2. Which of the following statement is correct?

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(D) Both (A) and (B)

(B) The increase in air movement increases the evaporation from the human body.

3. Most thermostatic expansion valves are set for a superheat of

5°C

10°C

15°C

20°C

4. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

2.33

3.33

1.33

4.33

5. The capillary tube, as an expansion device, is used in

Water coolers

Room air conditioners

Domestic refrigerators

All of these

6. The condition of refrigerant after passing through the condenser in a vapour compression system is

Saturated liquid

Superheated vapour

Wet vapour

Dry saturated vapour

7. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Positive

Zero

None of these

Negative

8. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

9. Which of the following cycles uses air as the refrigerant?

Ericson

Bell Coleman

Stirling

Carnot

10. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 1

1: 3

1: 9

9: 1

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11. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Equally

Unpredictable

Less

12. Rating of a domestic refrigerator is of the order of

5 tons

10 tons

40 tons

0.1 ton

13. Highest temperature encountered in refrigeration cycle should be

Above critical temperature

Much below critical temperature

At critical Temperature

Near critical temperature of refrigerant

14. The operating pressure for refrigerating units using R-12 as a refrigerant is

15 bar

30 bar

8 bar

2 bar

15. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.67

0.376

0.4

0.6

16. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Super-cooling

Normal cooling

None of these

Sub-cooling or under-cooling

17. The value of C.O.P in vapour compression cycle is usually

Equal to unity

Any one of the above

Always more than unity

Always less than unity

18. The bank of tubes at the back of domestic refrigerator is

Evaporator tubes

Refrigerant cooling tubes

Condenser tubes

Capillary tubes

19. The vapour compression refrigerator employs the following cycle

Carnot

Reversed Rankine

Rankine

Reversed Carnot

20. The domestic refrigerator uses following type of compressor

Axial

Miniature sealed unit

Piston type reciprocating

Centrifugal

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21. In a refrigeration system, heat absorbed in comparison to heat rejected is

More for small capacity and less for high capacity

Less

Same

22. Cooling water is required for following equipment in ammonia absorption plant

Evaporator

Condenser, absorber and separator (rectifier)

Absorber

Condenser

23. In a refrigeration system, the expansion device is connected between the

Compressor and condenser

Receiver and evaporator

Evaporator and compressor

Condenser and receiver

24. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Detect liquid in vapour

Collect liquid refrigerant and prevent it from going to compressor

Collect vapours

Superheat the vapour

25. The curved lines on a psychrometric chart indicates

Dry bulb temperature

Dew point temperature

Wet bulb temperature

Relative humidity

26. In a lithium bromide absorption refrigeration system

Ammonia is used as a refrigerant and lithium bromide as an absorbent

None of these

Lithium bromide is used as a refrigerant and water as an absorbent

Water is used as a refrigerant and lithium bromide as an absorbent

27. A thermostatic expansion valve in a refrigeration system

Ensures the evaporator completely filled with refrigerant of the load

Is suitable only for constant load systems

None of the above

Maintains different temperatures in evaporator in proportion to load

28. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

1.25

5.12

2.15

29. The boiling point of ammonia is

-30°C

-77.7°C

-33.3°C

-10.5°C

30. The freezing point of sulphur dioxide is

-77.7°C

-56.6°C

-135.8°C

-75.2°C

Page 4 of 4

31. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(D) Difference of (A) and (B)

(B) Heat stored in the human body

(A) Heat dissipated to the surroundings

32. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Involves no change in volume

Takes place at constant pressure

Takes place at constant temperature

Takes place at constant entropy

33. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Brine

Freon

Ammonia

Carbon dioxide

34. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

35. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₁ - T₂)/T₁

T₂/ (T₂ - T₁)

(T₂ - T₁)/T₁

T₁ / (T₂ - T₁)

36. For obtaining high COP, the pressure range of compressor should be

Any value

Low

Optimum

High

37. A bootstrap air cooling system has

Three heat exchangers

One heat exchanger

Two heat exchangers

Four heat exchangers

38. Critical temperature is the temperature above which

Water will evaporate

A gas will immediately liquefy

A gas will never liquefy

Water will never evaporate

39. Which of the following is not a desirable property of a refrigerant?

Low boiling point

High risibility with oil

Large latent heat

Good electrical conductor

40. Freon group of refrigerants are

Nontoxic and non-inflammable

Inflammable

Toxic

Non-inflammable and toxic

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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